The human activity most widely viewed as changing the planet is the burning of fossil fuels. ... to melt, threatening water supplies for hundreds of millions of people. ... and phosphorus to the biosphere than would occur naturally. ... compounds that can remain active in the environment for thousands of years .
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Answer:
2. A
3. A
4. C
5. Sorry I'm not sure on this one... I know it's NOT A. (I think it might be B: Both disciplines involve fieldwork.)
Explanation:
They crossed into North America from Asia to discover more of the region land, grow crops, and learn more about where they were living.